The present invention generally regards the coating of work-pieces. More particularly, the present invention regards method and system for precision coating implantable medical appliances.
The positioning and deployment of medical appliances within a target site of a patient is a common, often-repeated procedure of contemporary medicine. These appliances or implants are used for innumerable medical purposes including the reinforcement of recently re-enlarged lumens and the replacement of ruptured vessels.
Coatings are often applied to these medical appliances to increase their effectiveness. These coatings may provide a number of benefits including reducing the trauma suffered during the insertion procedure, facilitating the acceptance of the medical appliance into the target site, and improving the post-procedure effectiveness of the appliance.
Expandable stents, stent grafts, balloon delivery systems, and aneurism coils are specific examples of medical appliances or implants that may be coated and inserted within the body. Expandable stents are tube-like medical appliances that often have a mesh-like structure designed to support the inner walls of a lumen. These stents are typically positioned within a lumen and, then, expanded to provide internal support for it. Because of the direct contact of the stent with the inner walls of the lumen, stents have been coated with various compounds and therapeutics to enhance their effectiveness.
When this coating is haphazardly applied or has somehow been removed during the stent""s manufacture or delivery, the stent""s effectiveness can be compromised. In certain circumstances, defective implanted stents must be removed and replaced through a second medical procedurexe2x80x94an unwanted result.
Indiscriminate coating methods such as dip-coating and spray-coating have been used to coat stents as well as other medical appliances. These methods are, however, both wasteful and difficult to control. For example, dipping can result in non-uniform application of the coating to the appliance, thereby placing more coating at one end or region of the stent and making it difficult to predict the dosage of therapeutic that will be delivered when the stent or other appliance is implanted. The indiscriminate nature of dipping is also problematic as it may lead to the cracking and crumbling of coating at the junctions, hinges, and flexing members of the mesh-like stents. The coating that covers the hinged portions of the stent is highly susceptible to be exfoliated because, as the stent is expanded, intolerable stresses may develop within the coating.
FIGS. 1 and 2 are illustrative of some of the concerns stemming from an indiscriminate coating process like dipping. In FIG. 1 stent 11 is shown in a closed, pre-deployment state. Here, the stent 11 has been previously dipped in a vat of therapeutic in the direction of arrow 16. In other words, the right side of the stent was the leading edge of the stent entering the dipping vat. As can be seen, the coating of stent 11 is heavier on the right side of the stent 11 than on the left side and covers each of the junctions 13 throughout the entire stent 11. As can also be seen, the coating becomes progressively thicker and covers more of the space between each of the struts 12 as one travels from the left side of the stent 11 to the right side of the stent 11. This increasing thickness of coating is indicative of a stent 11 that has been dipped and left stand on one of its ends as the coating dries and adheres to the stent 11.
FIG. 2 shows the unevenly coated stent 11 of FIG. 1 in an expanded state as it may be after it is positioned within the body. As is evident, the expansion of stent 11 has led to the cracking and crumbling of coating 15. Also evident is that the coating has been removed from most if not all of the junction points 13 after the stent has been expanded.
System and method for coating a medical appliance is provided. In accord with one embodiment, a system for applying a coating to a medical appliance having accessible patterned surfaces is provided. This system may include: a processor, a support, and a bubble jet printing head having individual printing nozzles. In this system the support may be adapted to hold the medical appliance and to provide direct access for a coating to contact the exposed external patterned surfaces of the medical appliance. The bubble jet printing head in this system may move with respect to the medical appliance and may be in communication with a source of coating and with the processor. The processor in this system may contain commands that instruct the bubble jet printing head to force coating onto the accessible patterned surfaces of the medical appliance in a pattern that correlates with the accessible patterned surfaces of the medical appliance.
A method for applying a coating to a medical appliance having an accessible patterned surface is also provided. In one embodiment this method may include holding the medical appliance, providing direct access to the external surfaces of the medical appliance, and receiving command signals that instruct the bubble jet printing head to force coating onto the accessible patterned surfaces of the medical appliance in a pattern that correlates with the accessible patterned surfaces of the medical appliance.